Graphene is a two-dimensional nanostructure of covalently bonded carbon atoms and exhibits outstanding mechanical, electrical, and thermal properties. Graphene flakes consist of single or several graphene sheets exfoliated from graphite. Graphene flakes have been reconstituted into bulky structures that have a modulus of elasticity exceeding that of flexible graphite while possessing high strength.
A major challenge for graphene structures with high strength and toughness is to maintain the inherent active surface of graphene by preventing restacking of graphene tending to form close-packed layer structures. Single-layer graphene or a graphene flake has a wrinkled structure due to high area-to-thickness ratio thereof, but a graphene paper or composite including a large amount of graphene usually has a dense layer structure similar to graphite. The dense layered structure of graphene is an obstacle in achieving maximum mechanical properties owing to the short length of graphene that reduces the van der Waals force and tensile strength between graphene layers (by 1% or less).
There are some reports on complexes including less than 1% of graphene whose wrinkled structure is maintained. However, there is no report regarding the development of composite fibers including graphene alone or at a considerable concentration while maintaining the wrinkled structure of graphene.
The dense layered structure of graphene composites limits application thereof to energy and hydrogen storage media. For these reasons, there is a need to improve the porosity, mechanical properties and electrochemical properties of graphene structures.